Epoxy siloxane compositions useful for application as coating materials are well known, and have gained commercial acceptance as protective and decorative coatings for steel, aluminum, galvanizing, wood and concrete in maintenance, marine, construction, architectural, aircraft and product finishing markets. While epoxy-based compositions have long been known for their desired properties of good adherence to substrates, corrosion resistance, and chemical resistance, and weatherability, they have suffered from less than ideal properties of weatherability and related gloss retention. Epoxy siloxane compositions were developed to provide improved properties of weatherability and gloss retention without sacrificing the desired properties of corrosion resistance and chemical resistance.
U.S. Pat. No. 4,250,074 discloses a known epoxy siloxane composition comprising an interpenetrating polymer network (IPN) of intertwined epoxy polymers and polysiloxane polymers. The composition is prepared by simultaneously polymerizing, at substantially balanced reaction rates, a mixture of epoxy resin and silane groups to form two intertwined networks of polymerized epoxy and polysiloxane throughout a resulting coating. An amine curing agent is used to form the polymerized epoxy network, and water is distributed throughout the mixture to cause hydrolytic polycondensation of silane groups to form the polysiloxane. While this epoxy siloxane coating composition displayed improved properties of weatherability, corrosion and chemical resistance when compared to conventional nonsiloxane-containing epoxy resin compositions, it is known to be somewhat brittle, lacking a desired degree of impact resistance, flexibility and abrasion resistance for certain applications.
U.S. Pat. No. 5,618,860 discloses a known epoxy polysiloxane composition for use as a coating. The composition is prepared by combining a non-aromatic epoxy resin with a difunctional aminosilane hardener, an organotin catalyst, and an optional pigment. The so-formed epoxy polysiloxane composition provided improved properties of weatherability, chemical and corrosion resistance, and impact resistance when compared to conventional nonsiloxane-containing epoxy resin compositions. While this epoxy siloxane coating composition provided such improved performance properties, like the epoxy siloxane composition discussed above, it too is known to be somewhat brittle, lacking a desired degree of impact resistance, flexibility and abrasion resistance for certain applications.
It is, therefore, desired that an epoxy siloxane composition be developed that is both capable of providing the desired properties of weatherability, corrosion and chemical resistance already associated with epoxy siloxane compositions, while also providing improved properties of impact resistance, flexibility and abrasion resistance. It is desired that epoxy siloxane compositions of this invention provide improved resistance to cracking and delamination when applied in the form of coatings.